Age dependency of the cariporide-mediated cardio-protection after simulated ischemia in isolated human atrial heart muscles

Quercetin-modulated erythrocyte membrane sodium-hydrogen exchanger during human aging: correlation with ATPase's

CONTENT

Quercetin uptake by erythrocytes is rapid. The sodium-hydrogen exchanger (NHE) is a secondary active transporter, regulating intracellular pH, Na(+) concentration and cell volume.

OBJECTIVE

The aim of present study was to investigate NHE as a function of human age and effect of quercetin on its activity. The NHE activity was correlated with erythrocytes ATPases.

MATERIALS AND METHODS

We analyzed normal, healthy subjects of both sexes (20-82 years). NHE activity was estimated in terms of amiloride-sensitive H+-efflux from acid-loaded cells.

RESULTS

A significant age-dependent increase in NHE activity was observed during aging in humans. Concentration (10(-3 )M to 10(-8 )M)-dependent in vitro treatment with quercetin causes inhibition of NHE activity. The Na(+)/K(+) -ATPase (r = 0.8882) and Ca(2+)-ATPase (r = 0.9540) activities positively correlated with it.

DISCUSSION AND CONCLUSION

The present data show an additional mechanism where dietary flavonoids may exerts beneficial effect during aging.

Protein glycation - Between tissue aging and protection

Non-enzymatic formation of advanced glycation endproducts (AGEs) is associated with degenerative diseases. Chronic accumulation of AGEs with age in tissues especially in the extracellular matrix is well known and at least in part responsible for e.g., collagen crosslinking, tissue stiffening and thus induction of high blood pressure or diastolic heart failure. Binding of soluble AGEs to the receptor for AGEs, RAGE, induces an inflammatory response whereas the soluble form of RAGE (sRAGE) can inhibit inflammatory tissue injury like arteriosclerosis in mouse models. However, there are a number of indications that AGEs have protective effects as well. AGEs may inhibit lung tumor growth, glyoxal induced AGE modification of human heart muscle can reduce an ischemia reperfusion injury and AGEs from nutrition can reduce ROS induced cell damage.

CONCLUSIONS

In summary, this indicates that protein glycation behaves like a double-edged sword. It induces tissue aging and degenerative diseases on the one hand, on the other hand, may also have protective effects, indicating a hormetic response.

NHE isoform switching and KChIP2 upregulation in aging porcine atria

Aging increases the risk of cardiac pathologies including atrial fibrillation and can alter myocardial responsiveness to therapeutic agents. Here, seeking molecular correlates of myocardial aging processes, we performed global “whole transcript” analysis of 25,388 genes using 572,667 probes to compare the left atrial (LA) transcriptomes of young adult (9 months old) versus elderly (10 years old) female swine. NHE2 (>9-fold) and KChIP2 (3.8-fold) exhibited the highest aging-related expression increases. Real-time qPCR recapitulated these findings and indicated a 50% decrease in LA NHE1, a twofold increase in right atrial KChIP2, but no significant changes for these transcripts in either ventricle. Notably, even in young adult pigs, NHE2 transcript was detectable and enriched in the atria over the ventricles. NHE1, the recognized cardiac isoform of the sodium hydrogen exchanger, has proven a compelling but clinically disappointing therapeutic target with respect to reperfusion arrhythmias. Our data challenge the dogma that NHE1 is alone in the myocardium and suggest that NHE2 could negatively impact the pharmacological responsiveness of atrial tissue to NHE1-specific inhibitors. KChIP2 is a cytosolic β subunit essential for generation of I_to. The increased KChIP2 expression we observed with aging substantially shortened in silico atrial myocyte action potential duration, a predisposing factor in atrial fibrillation. Consistent with this, 4/5 elderly swine sustained pacing-induced AF≥15 s after cessation of stimulation, compared to 0/3 young swine. Our findings uncover potential molecular bases for increased arrhythmogenicity and reduced pharmacologic efficacy in the aging atrium, in a large animal model of human cardiac physiology.

Middle age aggravates myocardial ischemia through surprising upholding of complex II activity, oxidative stress, and reduced coronary perfusion

Aging compromises restoration of the cardiac mechanical function during reperfusion. We hypothesized that this was due to an ampler release of mitochondrial reactive oxygen species (ROS). This study aimed at characterising ex vivo the mitochondrial ROS release during reperfusion in isolated perfused hearts of middle-aged rats. Causes and consequences on myocardial function of the observed changes were then evaluated. The hearts of rats aged 10- or 52-week old were subjected to global ischemia followed by reperfusion. Mechanical function was monitored throughout the entire procedure. Activities of the respiratory chain complexes and the ratio of aconitase to fumarase activities were determined before ischemia and at the end of reperfusion. H(2)O(2) release was also evaluated in isolated mitochondria. During ischemia, middle-aged hearts displayed a delayed contracture, suggesting a maintained ATP production but also an increased metabolic proton production. Restoration of the mechanical function during reperfusion was however reduced in the middle-aged hearts, due to lower recovery of the coronary flow associated with higher mitochondrial oxidative stress indicated by the aconitase to fumarase ratio in the cardiac tissues. Surprisingly, activity of the respiratory chain complex II was better maintained in the hearts of middle-aged animals, probably because of an enhanced preservation of its membrane lipid environment. This can explain the higher mitochondrial oxidative stress observed in these conditions, since cardiac mitochondria produce much more H(2)O(2) when they oxidize FADH(2)-linked substrates than when they use NADH-linked substrates. In conclusion, the lower restoration of the cardiac mechanical activity during reperfusion in the middle-aged hearts was due to an impaired recovery of the coronary flow and an insufficient oxygen supply. The deterioration of the coronary perfusion was explained by an increased mitochondrial ROS release related to the preservation of complex II activity during reperfusion.

KATP channel blocker does not abolish the protective effect of Na+/H+ exchange 1 inhibition against ischaemia/reperfusion in aged myocardium

BACKGROUND AND OBJECTIVE

Ageing is associated with an increase in myocardial susceptibility to ischaemia/reperfusion (I/R) injury. Na+/H+ exchange (NHE) inhibition and anaesthetic preconditioning (APC) are shown to protect myocardium from I/R injury. We set out to investigate whether NHE inhibition can induce protection against I/R injury and whether KATP channel inhibition can enhance this effect in aged rat myocardium.

METHODS

Hearts from 24-month-old rats were assigned to four groups: control group; APC group perfused with 2.5% sevoflurane before ischaemia; HOE group perfused with (3-methylsulfonyl-4-piperidinobenzoyl) guanidine methanesulfonate (HOE-694) prior to ischaemia; and HOE+5HD group perfused with both HOE and 5-hydroxydecanoic acid before ischaemia. We measured intracellular Na+ and Ca++ to quantitate the severity of myocardial injury.

RESULTS

Both intracellular Na+ and Ca++ were significantly increased at the end of ischaemia and both were attenuated by NHE inhibition. Intracellular Na+ was 134 +/- 12 mEq kg(-1) dry weight in control group and 55 +/- 7 in HOE group (P < 0.05). Intracellular Ca++ was 1764 +/- 142 nmol l(-1) in control group and 694 +/- 213 in HOE group (P < 0.05). Infarct size was measured at 28 +/- 4% in control group vs. 17 +/- 2% in HOE group (P < 0.05). High-energy phosphates and myocardial function were better preserved in HOE group compared with control (P < 0.05). The beneficial effect of HOE on myocardial preservation was not blocked by 5HD nor were there any differences between APC and control groups.

CONCLUSION

NHE inhibition was effective in protecting myocardium from I/R injury in aged rats, whereas APC was not. 5HD failed to block the protective effect of NHE inhibition.

Occult Cardiotoxicity—Toxic Effects on Cardiac Ischemic Tolerance

The outcome of cardiac ischemic events depends not only on the extent and duration of the ischemic stimulus but also on the myocardial intrinsic tolerance to ischemic injury. Cardiac ischemic tolerance reflects myocardial functional reserves that are not always used when the tissue is appropriately oxygenated. Ischemic tolerance is modulated by ubiquitous signal transduction pathways, transcription factors and cellular enzymes, converging on the mitochondria as the main end effector. Therefore, drugs and toxins affecting these pathways may impair cardiac ischemic tolerance without affecting myocardial integrity or function in oxygenated conditions. Such effect would not be detected by current toxicological studies but would considerably influence the outcome of ischemic events. The authors refer to such effect as “occult cardiotoxicity.” In this review, the authors summarize current knowledge about main mechanisms that determine cardiac ischemic tolerance, methods to assess it, and the effects of drugs and toxins on it. The authors offer a view that low cardiac ischemic tolerance is a premorbid status and, therefore, that occult cardiotoxicity is a significant potential source of cardiac morbidity. The authors propose that toxicologic assessment of compounds would include the assessment of their effect on cardiac ischemic tolerance.